What is the standard sideband for JT65, JT9, FT4, or FT8 digital signal when using AFSK?
Why Nearly all modern digital modes sent as audio frequency-shift keying through an SSB transmitter use upper sideband, and the WSJT-X family (JT65, JT9, FT4, FT8) is no exception. With USB the transmitted RF frequency equals the dial frequency plus the audio tone frequency, so tones map in the same order on every band and everyone's decoder agrees on the signal's position in the passband. If one station used LSB the tone ordering would invert and the transmission would not decode.
Watch out The choice that says LSB reflects the voice convention on 160, 80 and 40 meters, but that tradition applies only to phone; digital operation stays on USB on all bands. DSB and SSB are not sideband selections a transceiver offers for these modes.
Digital is always Upper, on every band. Voice switches sidebands, data does not.